Bluebox Security, a stealth startup focusing on securing mobile devices in the enterprise, says it has raised an $18 million Series B round of venture capital funding led by Tenaya Capital. Tenaya’s Brian Melton will join the Bluebox board of directors.

Bluebox hasn’t said exactly what it’s doing, but it has made clear that it’s wrestling with the security implications of the BYOD or “bring your own device,” movement that has emerged as a popular way for companies to handle making their employees more productive on mobile devices.

The problem emerges when employees mix their personal and work lives on those phones: Sometimes they may download apps that pose a security risk to sensitive company data. A Forrester survey from 2012 found that about 85 percent of employees who use personal devices on the job do this, and logic tells you that has to be a low estimate. The use of public Wi-Fi networks is another risk.

Bluebox has said in corporate blog posts that customers will use its product to protect corporate data across open networks; use it to ensure that it can only be accessed by people with known credentials; and that the use of corporate data will be tracked.

In the company’s announcement on the funding, CEO Caleb Sima says while most mobile security products focus on the device, Bluebox will focus on the data that’s usually targeted for theft. “We founded Bluebox with a unique approach to mobile security that focuses on what really matters—data,” he said.

The company got a lot of attention when its researchers discovered what they described as a “master key,” security vulnerability Google’s Android mobile operating system that affected about 900 million phones.

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